TY - JOUR
AU - Faw, Fred L.
AB - An Automatic Method for the Identification and Localization of Interstitial Objects 1 Physics Investigation Stephen Balter , M.S. , Gian D. Ragazzoni , B.S. , John S. Laughlin , Ph.D. and Fred L. Faw , B.S. Excerpt A radiographic localization apparatus and an ancillary computer program have been developed to automate the dosimetry of interstitial and intracavitary implants. The apparatus consists of a rigid frame supporting two permanently mounted x-ray tubes, two close-fitting orthogonal cassette holders, fixed grids, and phototimers. Film planes and co-ordinates of the focal spots are known with respect to a set of axes fixed at the frame. Experience with the preliminary apparatus has demonstrated the absolute necessity of accurate (to within 0.5 mm) knowledge of these geometric constants. The essentials of this localization system are shown in Figure 1. A pair of orthogonal radiographs of the implanted region is obtained. The co-ordinates of each source image are determined and referred to the apparatus co-ordinate system. No attempt is made to correlate images with each other. The computer "draws" lines connecting the image of each source on the anteroposterior radiograph with the overhead focal spot. A line is "drawn" between one of the images on the lateral radiograph and the lateral focal spot. The intersection of this lateral line with one of the anteroposterior lines identifies the anteroposterior image corresponding to the given lateral image. The point of intersection of these two lines defines the spatial co-ordinates of the source. The spatial co-ordinates of each source are obtained in this manner. The two radiographs must be exposed simultaneously and rapidly so that excessive source motion is avoided. The problem of balancing exposure time against focal spot size for minimum system error has been examined but not as yet solved. An added complication is the requirement that there be high contrast of the sources on the radiographs, and this necessitates the use of low kVp and high mAs. “Intersection” is defined by the computer program as the place where the shortest distance between two lines is less than one millimeter. Because the rate of change of the distance between the two lines, as the distance along the lines from the point of intersection increases, is proportional to the sine of the angle between them, the system sensitivity and accuracy are a maximum for orthogonal radiographs. This system is immediately adaptable to related problems (foreign body localization, bone size determination, and pelvimetry), provided adequate landmarks exist.
TI - An Automatic Method for the Identification and Localization of Interstitial Objects
JF - Radiology
DO - 10.1148/88.1.152b
DA - 1967-01-01
UR - https://www.deepdyve.com/lp/radiological-society-of-north-america-inc/an-automatic-method-for-the-identification-and-localization-of-C4kWWTiUGg
SP - 152
VL - 88
IS - 1
DP - DeepDyve
ER -